Pests cause a great loss to major agricultural products and various useful plants every year. To control the pests, 1,205 kg/km2/year of agricultural chemicals (pesticides) have been used in Korea since mid 1990s, which is 4.6 fold much as average amount (263 kg) used in OECD countries and 48 times much as a minimum 25 kg used in New Zealand. Mostly organic pesticides and chemical insecticides have been used, resulting in the destruction of ecosystem, underground water-contamination, increased toxicity remaining in agricultural products and the appearance of pests having strong resistance. Countries brought about an agreement to reduce organic pesticide quantity used every year about 50% until 2004 at Rio environmental conference held in 1992. In fact, 46% of conventional organic insecticides, especially 68% in vegetables and fruits growing fields, were substituted with alternative pesticides in the United States in 1997, in order to control pests with less damage to environment.
A pest controlling method using insect pathogenic microorganism is an environmental protective control means that works selectively for target pests only, prohibits the appearance of pests having resistance, is available lastingly and makes possible to produce agricultural products in good quality without residual toxicity and without harming human, animals, plants and environment. Thus, many advanced countries in the field of agriculture including US have been separated insect pathogenic microorganisms suitable for their own countries' condition, mass-produced and put to use thereof actually.
Though the environmental protective biotic pesticide takes just about 5% of total pesticide market, it grows as fast as more than 20% every year owing to the recognition of importance of biotic pesticide. So, biotic pesticides are expected to take huge part of the market in years. When domestic market is open for alternative pesticides, it will be taken over by countries that have already developed biotic pesticides using insect pathogenic microorganisms since Korea has depended on only organic pesticides. Then, Korea's foreign exchange holdings will be decreased and export of domestic agricultural products produced by chemical pesticides will be obstructed. In order to cope with such difficult situation effectively, it is urgently required to develop biotic (microbial) pesticides using insect pathogenic microorganisms suitable for our agricultural environment.
As a kind of soil pests, Mimela splendems (gold bug) is a euryphagous pest harming plants, especially plants of Rossaceae, Salicaceae, Fagaceae, Betulaceae and Aceraceae. Some adults of soil pests harm leaves of crops or plants and larvae do roots of various crops and grass. The gold bugs damage not only various broad-leaved trees in forest but general crops like corns or tomatoes, fruits like apples or apricots, flowers like chrysanthemums or roses, tea plants, many herbs, ginseng farms, etc (Lee et al, Korean Journal of Applied Entomology, 1997, 36, 2, 156-165).
The larvae of gold bugs developing and living in golf courses directly harm grass roots to death and indirectly provide themselves as feed for birds, causing digging up the grass. Therefore, they have a bad effect on the preservation of grass quality (Chu et al, Korean Journal of Turfgrass Science, 1998, 12, 3, 225-236; Lee et al, Korean Journal of Applied Entomology, 1997, 36, 2, 156-165; Lee, PhD Thesis, 2000). To control such soil insects like gold bugs, fenitrothion emulsion, chlorpyrifos-methyl emulsion and ethoprophos granules have been used. But those chemical pesticides have effects on only just-hatched larvae (the first larva stage). Thus, catching the right time is essential for controlling those insects. By the way, those chemical pesticides weaken the grass and cause overdose (Korea Patent Application #1999-15472).
Great efforts have been made to control soil pests like gold bugs, Encarcia formosa, Eretmocerus eremicus, Plutella xylostella, Spodoptera litura and Nilaparvata lugens. But using the conventional chemical pesticides causes not only high expense but also such problems that the destruction of ecosystem, the under water contamination, the residual toxicity in agricultural products and the appearance of insects having resistance.
Thus, in order to develop an environmental protective controlling method, the present inventors have searched insect pathogenic microorganisms that are good for controlling soil pests especially harming major agricultural products and confirmed that a fungus of Metarhizium genus kills soil pests including the larvae of gold bugs. So, the present inventors have completed the present invention by preparing a microbial insecticide comprising the fungus of Metarhizium genus for controlling soil pests.